stats: Add comment about MAP_SHARED

Clarify why MAP_SHARED is used instead of the obvious MAP_PRIVATE.

diff --git a/src/stats.c b/src/stats.c
index 929e09b..679a372 100644 (file)
--- a/src/stats.c
+++ b/src/stats.c
@@ -286,6 +286,12 @@ static int stats_file_remap(struct stats_file *file, size_t size)
        }
 
        if (file->addr == NULL) {
+               /*
+                * Though the buffer is not shared between processes, we still
+                * have to take MAP_SHARED because MAP_PRIVATE does not guarantee
+                * that writes will hit the file eventually. For more details
+                * please read the mmap man pages.
+                */
                addr = mmap(NULL, new_size, PROT_READ | PROT_WRITE,
                                MAP_SHARED, file->fd, 0);
        } else {